1. Field of the Invention
This invention relates to silicone rubber-covered rolls. More particularly, this invention relates to rolls formed by coating a roll axle with a composition that cures to form a silicone rubber having a hardness and compression set within specified limits. The rolls can be used as fixing rolls in electrophotographic copiers and paper feed rolls in facsimile machines.
2. Description of the Prior Art
A number of contact thermal fixing methods are used in electrophotographic copiers. These methods typically involve electrophotographically forming an image from a thermoplastic resin powder, usually referred to as toner, on a photoreceptor. This image is subsequently transferred to transfer paper, and the copied image is produced by melting and fusing the toner particles using a fixing element. These elements include a heated hard roll exhibiting both heat resistance and releasability, and a soft press roll, which is a typically a silicone rubber-covered roll having heat resistance, releasability, and flexibility. To fix the toner image, these two types of rolls are pressed together under a prescribed pressure, and the image-carrying transfer paper is then passed between them.
The problems that arise in these contact thermal fixing methods include creasing of the transfer paper, and blurring of the image.
The present inventors discovered the main reason for a blurred image on the transfer paper is that the optimal contact area needed for the production of a clear image cannot be maintained. Because the soft roll is continually subjected to compressive deformation, the silicone rubber layer readily undergoes compression set, which changes the contact area of the soft roll.